strange problems

I have a Mendel with the latest Marlin formware, RAMPS 1.4, 20 x 4 LCD, encoder and SD card reader set up as Ultipanel and using Pronterface as driver. I have 2 odd problems and one query. 1. for some reason my printer has a aversion to printing more than about 2.5mm high... it prints fine up to there but then the Z axis rises one increment and then descends one increment sequentially so that it never actually goes any higher and just keeps smearing the plastic across the top of the print at that height. Homing works perfectly from either Pronterface or the encoder but sending a G1 Z20 F50 from Pronterface just causes the Z-steppers to whine and not move. I don't know whether these problems are linked and may be interference between the Ultipanel and Pronterface.... which brings me to the query and the reason I am still trying to use Pronterface... the Ultipanel menus don't have any means of raising the Z-axis...Why?
2. I am also trying to set the machine up with auto bed levelling but I can't get a servo to work... I have modified Config.h appropriately and added told Marlin.h to include the servo.h library which appears to be working in that sending a M280 P0 S150 instruction from Pronterface causes the signal pin of the servo pins on the RAMPS to increase its voltage w.r.t. ground. However, when I plug a servo in, the 5 volts power on the servo pins drops to 2 volts and so. while I assume this is the problem, I cannot think how to cure it or where to look for the problem. Needless to say, the mini 9G servos I have tried have all checked out OK on a servo tester. Power to the Arduino is via the USB plug although plugging in an additional battery supply doesn't seem to make any difference, and to the RAMPS 1.4 is from an X-box power supply giving 12v at 14.5Amps - I assume the latter supplies the 5volts for the RAMPS board including the servos. I would be grateful of any help or advice. thanks, Ian

Z-axis acceleration may be too high.

The z should be available on the panel if you select the .1mm or 1mm increments.

Use a 7805 to power the servo.

Thanks Stephen, Z-acceleration is set at 1000 in config.h - I tried it down at 500 but it made no difference. I don't understand how it could be this as homing works perfectly. Also, it doesn't seem to make any difference what speed value I attach to the G-code instruction - the high pitched whine is pretty much the same frequency. G-code printing works OK for the first 10 or 12 layers and gives a good result to that point. The printer worked fine until I added the LCD etc. but now I don't even seem to be able to go back to where I was before.

I'll check the Z increment thing..

I'll try a 7805 on an external board - what I couldn't understand is why the power on the servo pins is being pulled down while the voltage on things like the LCD, SD card reader etc. still reads the full 5v. I assume I can feed the 5v from the 7805 to the servo power jumper pin on the RAMPS or should I take the servo connectors out to a different board?

Still a bit confused....

I should also say that I first suspected that the Z drive problem may have been caused by the stepper driver so I swapped the Pololu board and it made no difference..

You need to change the z acceleration to about 125 this should solve your home problem.
Dont have anything for your other.

Quote
bassman
I assume I can feed the 5v from the 7805 to the servo power jumper pin on the RAMPS or should I take the servo connectors out to a different board?

I have a 7805 connected into the 5A connector and the output connected to the servo power 5v pin which is between the VCC and PS-ON.

is your z-height set correctly in the configuration file?

Have you looked at the end stop on your Z axis?

Thanks everyone. I have confirmed that an external 5v supply will solve the servo problem. The Z height is set correctly and, by jiggling a few values in speed and acceleration I can now jog the Z axis up by several tens of mm from Pronterface reliably, however, I am still having some problems in trying to jog the Z axis up using the encoder through the Marlin menu system. Movement seems unpredictable and a bit random - again it may be somehow linked to speed and acceleration as it seems that, some of the time, only one or other of the 2 z motors moves even though they are wired in parallel. The odd thing is that its not always the same motor which fails to move... hopefully I'll get back to making good prints sometime this year!!.

I thing your z issue is in your movement settings. Note there there are separate speed settings for homing or manual moves and print moves. You'll have to play around with those. I suspect the issue is with your print movement settings, not your homing/manual movement settings since you say it homes perfectly.

Most importantly, something to be mindful of is if you have your EPROM turned on, your EPROM settings in your driver software will override any firmware changes you make. Therefore your test results won't change unless you either turn off EPROM or restore your EPROM settings to factory in your driver software. You can find the EPROM setting in your Cofiguration.h tab . I've copied the section below...

//===========================================================================
//=============================Additional Features===========================
//===========================================================================

// EEPROM
// The microcontroller can store settings in the EEPROM, e.g. max velocity...
// M500 - stores parameters in EEPROM
// M501 - reads parameters from EEPROM (if you need reset them after you changed them temporarily).
// M502 - reverts to the default "factory settings". You still need to store them in EEPROM afterwards if you want to.
//define this to enable EEPROM support
//#define EEPROM_SETTINGS
//to disable EEPROM Serial responses and decrease program space by ~1700 byte: comment this out:
// please keep turned on if you can.
#define EEPROM_CHITCHAT